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Burrows attributed to the lysorophid Brachydectes elongatus occur within a green mudstone lens in the Lower Permian (Wolfcampian) Speiser Shale (Council Grove Group) of eastern Kansas. The burrow-bearing unit consists of a 100 m long lens of massive, calcareous, silty mudstone with a maximum thickness of 35 cm. The lens also contains the fossils of fish, amphibians, reptiles, charophytes (Stomachara), and ostracodes (Carbonita). The mudstone lens pinches out laterally into red, pedogenically modified mudstone. The burrows occur in three layers. At the top of each layer is a subaerial exposure surface indicated by rhizoliths, mudcracks, and coarse-grained lags. The mudstone lens is interpreted as the deposit of a shallow, ephemeral pond. The burrows occur in three vertically and temporally separated clusters with concentrations up to 20/m2. The burrows show two types of architecture. Type I burrows are elongate, elliptical tubes 4–32 cm long and 2–7 cm in width. Type II burrows are short, elliptical tubes 1.5–3.5 cm in length and 2.5–5 cm in width. The burrow fill consists of a mudstone capped by sandy siltstone. Each burrow layer contains a varying number of articulated and disarticulated lysorophid skeletons within the burrows and surrounding matrix. While similar to Permian lungfish burrows, the architecture and surficial morphology of the lysorophid burrows permits their distinction even in the absence of body fossils. The occurrence of burrow layers capped by subaerial exposure surfaces and separated by layers of non-burrowed, massive mudstone indicates that burrowing occurred in response to episodic, perhaps seasonal, droughts on the Permian coastal plain. The lysorophid burrowing behavior is analogous to that of the extant amphibians Amphiuma sp. and Siren intermedia, which inhabit rivers and ponds in the southeastern USA. [Copyright &y& Elsevier]

Burrows of the lysorophid amphibian Brachydectes elongatus occur in deposits interpreted as ephemeral ponds within the Lower Permian Speiser Shale of eastern Kansas. The burrows of B. elongatus have been previously recorded in the Lower Permian strata of Texas, Oklahoma, and Kansas, but have not been described in detail and an ichnotaxonomic designation has not been provided. Torridorefugium eskridgensis new ichnogenus and ichnospecies show two types of burrow architecture distinguished by width-to-length ratios. Type I burrows are elongate, elliptical tubes 4-32 cm long and 2-7 cm wide. Type II burrows are short, elliptical tubes 1.5-3.5 cm long and 2.5-5 cm wide. Both Type I and II burrows may contain coiled skeletons of B. elongatus. Torridorefugium eskridgensis occur in clusters of up to 45 burrows with maximum concentrations of 20/m². The type specimens of Torridorefugium eskridgensis occur in a 40-cm-thick lens of calcareous mudstone that fills a 100-m-long paleodepression within a well-developed paleosol. The burrow clusters are capped by surfaces with evidence of subaerial exposure, and overlain by nonburrowed, massive mudstone containing the fossils of the charophyte Stomachara, the ostracodes Carbonita and Paraparchites, fish, amphibians, and reptiles. This succession suggests that lysorophids burrowed in response to episodic, perhaps seasonal, droughts on the Permian midcontinental coastal plain. Permian lysorophid burrowing behavior is analogous to that of the extant aestivating amphibians Amphiuma sp. and Siren intermedia that inhabit ephemeral rivers and ponds of the southeastern United States. [ABSTRACT FROM AUTHOR]

Mosasaurs were widespread predators of the vast Cretaceous seas, and it is debated whether these extinct marine reptiles migrated to coastal environments to feed or reproduce. Here we investigate the potential for migration of mosasaurs through novel high-resolution sclerochronology that samples incremental growth lines in fossil mosasaur teeth and extracts oxygen isotopes from pristine enamel. Oxygen isotope trends of consecutive teeth are spliced to reconstruct one to seven month-long life histories of Platecarpus tympaniticus and Clidastes propython mosasaurs, respectively, collected from time-equivalent chalk deposits of the Western Interior Seaway and Mississippi Embayment of North America. The records of all individuals—two adults and one juvenile—are characterized by semi-regular depletions in oxygen isotope values, indicating travel from marine to freshwater coastal environments. Weekly to bi-weekly consumption of freshwater by two genera at diverse life stages implies that mosasaur osmoregulatory function was similar to their living sea snake relatives that drink freshwater periodically. • We reconstruct palaeoecology of mosasaurs from coeval Kansas and Alabama chalk. • Oxygen isotopes in pristine fossil tooth enamel record changing aquatic habitats. • Two adults and one juvenile show a pattern of bi-weekly migration to freshwater. • Freshwater consumption suggests osmoregulation similar to living sea snakes. [ABSTRACT FROM AUTHOR]